Two nickel-added poly(polyoxometalate)s built of Keggin-type {Ni6PW9} and Anderson-type NiW6O24via WO4/Sb2O bridges and Ni-O-W linkages with efficient hydrogen evolution activity

Two Ni-added poly(polyoxometalate)s built of Keggin-type {Ni6PW9} and Anderson-type NiW6O24 units via WO4/Sb2O bridges and Ni-O-W linkages, Na4H8[Ni(enMe)2][(Sb2O)2(NiW6O24)-{Ni12O2(OH)4(enMe)4(H2O)3(WO4)2(B-α-PW9O34)2}2]·39H2O (1) and H9[Ni(en)2(H2O)][Ni0.5(en)2(H2O)][Ni-(enMe)2(H2O)][(Sb2O)2(NiW6O24){Ni12O2(OH)4(en)2(enMe)2(H2O)3(WO4)2}-{Ni12O2(OH)4(en)4(H2O)3(WO4)2}(B-α-PW9O34)4]·45H2O (2), have been hydrothermally synthesized and characterized, in which the {Ni12(WO4)2(PW9)2} subunit was obtained by the synergistic directing effect of 2 lacunary PW9O34 (PW9) fragments and further linked by a central Anderson-type (Sb2O)2(NiW6O24) bridge. Both compounds represent the first example of Ni-added polyoxometalates (POMs) simultaneously based on Keggin-type and Anderson-type POM components. Photocatalytic studies revealed that 2 can work as an efficient heterogeneous catalyst towards a light-driven H2 evolution reaction, achieving a hydrogen evolution rate of as high as 19 214 μmol g-1 h-1 (TON = 1500), which is superior to most of the reported POM-based heterogeneous catalysts.

High-Nuclear Co-Added Polyoxometalate-Based Chain: Electrocatalytic Oxygen Production

A high-nuclear Co-added polyoxometalate (CoAP) was synthesized via a hydrothermal reaction: H14.5K9Na7.5-{[Co8(μ2-OH)(μ3-OH)2(H2O)2(Co(H2O)GeW6O26)(B-α-GeW9O34)2][BO(OH)2][Co12(μ2-OH)(μ3-OH)5(H2O)3(Co(H2O)GeW6O26)(GeW6O26)(B-α-GeW9O34)]}·46H2O (1). The polyoxoanion of 1 contains a large Co20 cluster gathered by lacunary GeW6O26 and GeW9O34 subunits. 1 represents a one-dimensional (1D) chain formed by adjacent polyoxoanions coupling through a CoO6 double bridge, showing the first example of a high-nuclear CoAP-based inorganic chain. 1 served as an efficient electrocatalyst in oxygen evolution reactions (OERs).

A Hexadecanuclear Cobalt-Added Tungstogermanate Containing Counter Cobalt Hydrates: Synthesis, Structure and Photocatalytic Properties

The synthesis and exploration of the properties of structurally-new polyoxometalates (POMs) has been attracting considerable research interest. In this work, a hexadecanuclear cobalt-added tungstogermanate, H₃₁(NH₄)₅Na₁₆{Co^Ⅲ(H₂O)₆}₄{[Co^Ⅱ₄(μ₃-OH)₃(PO₄)]₄(A-α-GeW₉O₃₄)₄}₂·23-H₂O (1), was synthesized under hydrothermal conditions and characterized by various techniques. Compound 1 can effectively drive the heterogeneous photocatalytic hydrogen evolution reaction in the presence of [Ir(ppy)₂(dtbbpy)][PF₆] as the photosensitizer, with triethanolamine (TEOA) and N-Hydroxy succinimide (NHS) used as the dual sacrificial reagents. Control experiments revealed the important role of NHS in enhancing the hydrogen-evolution activities. Under optimal catalytic conditions, a hydrogen yield of 54.21 μmol was achieved after 10-h photocatalysis, corresponding to a hydrogen evolution rate of 1807.07 μmol·g^-1·h^-1. Stability studies demonstrated that catalyst 1 can be isolated and reused for three successive photocatalytic cycles with negligible decline of the H₂ yield, indicating the stability and recycling robustness of catalyst 1.

40Ni-Added Poly(polyoxometalate) Assembled by {Ni6GeW9} and {Ni8(GeW9)2} Units: Structure, Magnetic, and Heterogeneous Catalysis Properties

A novel 40Ni-added germanotungstate, Cs₈K₁₄Na₃H₃{[Ni₆(OH)₃(H₂O)₆(B-α-GeW₉O₃₄)]₂[Ni₈(μ₆-O)(μ₂-OH)₂ (μ₃-OH)₂(H₂O)B₂O₃(OH)₂(B-α-GeW₉O₃₄)₂]}₂·84H₂O (1), was made by the reaction of the trivacant [A-α-GeW₉O₃₄]^10- ({GeW₉}) precursor with Ni²⁺ cations and B₅O₈^-, and systematically investigated by Fourier-transform infrared spectroscopy, elemental analysis, thermogravimetric analysis, and powder X-ray diffraction. Single crystal X-ray analysis indicates that the polyoxoanion of 1 is a novel octamer constructed by {Ni₆GeW₉} and {Ni₈(GeW₉)₂} structural building units via Ni-O═W linkages. The magnetic behavior shows the existence of overall ferromagnetic interactions among the Ni²⁺ centers in compound 1. Photocatalytic H₂ production studies have implied that 1 can work as a heterogeneous catalyst for hydrogen production with decent robustness and recyclability.

Structurally-New Hexadecanuclear Ni-Containing Silicotungstate with Catalytic Hydrogen Generation Activity

A structurally-new, carbon-free hexadecanuclear Ni-containing silicotungstate, [Ni₁₆(H₂O)₁₅(OH)₉(PO₄)₄(SiW₉O₃₄)₃]^19-, has been facilely synthesized using a one-pot, solution-based synthetic method systematically characterized by single-crystal X-ray diffraction and several other techniques. The resulting complex works as a noble-metal-free catalyst for visible-light-driven catalytic generation of hydrogen, by coupling with a [Ir(coumarin)₂(dtbbpy)][PF₆] photosensitizer and a triethanolamine (TEOA) sacrificial electron donor. Under minimally optimized conditions, a turnover number (TON) of 842 was achieved for TBA-Ni₁₆P₄(SiW₉)₃-catalyzed hydrogen evolution system. The structural stability of TBA-Ni₁₆P₄(SiW₉)₃ catalyst under photocatalytic conditions was evaluated by the mercury-poisoning test, FT-IR, and DLS measurements. The photocatalytic mechanism was elucidated by both time-solved luminescence decay and static emission quenching measurements.

High-Nuclear Ni-Substituted Poly(polyoxometalate) Containing an Anderson-like {Cs7} Cluster

A novel high-nuclear Ni-substituted poly(polyoxometalate) [poly(POM)], [H₂N(CH₃)₂]₂Na₁₈Cs₂H₁₃[(Cs₇(H₂O)₆)@{(PO₄)-@(Ni₄(OH)₃(WO₄))₃@(B-α-PW₉O₃₄)₃}₂]·30H₂O (1), has been successfully developed and structurally characterized. The polyoxoanion of 1 can be viewed as a unique huge sandwich structure made of an unprecedented Cs₇(H₂O)₆ ({Cs₇}) cluster core encapsulated by two trimeric [(PO₄)@(Ni₄(OH)₃(WO₄))₃@(B-α-PW₉O₃₄)₃]^21- subunits, in which the {Cs₇} cluster presents an interesting Anderson-like arrangement and is the first example of a classical POM configuration based on the alkali metal cluster in the POM chemistry. The polyoxoanion can also be described as an unusual [(Cs₇(H₂O)₆)@{(PO₄)@(Ni₄(OH)₃(WO₄))₃}₂]¹⁹⁺ cluster packaged by six {PW₉} fragments. Furthermore, investigations on the Knoevenagel condensation reaction reveal that 1 has good catalytic activity for the condensation of various aldehydes and malononitrile into corresponding products with excellent yields.

{Ti6}/{Ti10} Wheel Cluster Substituted Silicotungstate Aggregates

Two novel Ti-oxo wheel cluster substituted silicotungstates (STs) [H₂N(CH₃)₂]₉H₉[Ti₆O₆(SiW₁₀O₃₇)₃]·11H₂O (1) and [H₂N(CH₃)₂]₁₆H₁₀[Ti₁₀O₁₁(SiW₁₀O₃₇)₂(SiW₉O₃₅)₂]·14H₂O (2) have been made by hydrothermal reactions. The polyoxoanion of 1 is a ring-shaped trimer where a Ti₆O₆ ({Ti₆}) wheel cluster is encapsulated by three divacant [SiW₁₀O₃₇]^10- (SiW₁₀O₃₇) fragments. However, 2 is built by two divacant SiW₁₀O₃₇ units and two rare trivacant [SiW₉O₃₅]^12- (SiW₉O₃₅) fragments and further installs an unprecedented Ti₁₀O₁₁ ({Ti₁₀}) double-wheel cluster. To the best of our knowledge, 2 is rare in POM chemistry. Studies on the catalytic oxidation properties reveal that 1 exhibits high catalytic activity toward the oxidation of various sulfides using H₂O₂ as an oxidant. Furthermore, 1 can be facilely recycled and reused for at least five cycles without obvious loss of catalytic activity.

Two new hexa-Ni-substituted polyoxometalates in the form of an isolated cluster and 1-D chain: syntheses, structures, and properties

Two new hexa-Ni-substituted polyoxometalates are made and characterized, exhibiting electrochemical performance and photocatalytic activity for the degradation of organic dyes under UV irradiation.